[Autumn]

It seems that giant gene adds +10% weight to the base weight of weapons instead of the total weight, is this intentional?

Also it seems that Giant Gene also only adds +10% to base HP, is this also intentional?

[Neus]

Gigantic's (and all enchantment's) weight bonus will apply after everything but custom parts.

Gigantic's (and all enchantment's) HP bonus is applied early on in the maximum HP calculation, so it's possible certain bonuses are applied after it that aren't increased.